448-61-3Relevant articles and documents
On the Electron-Donating Properties of Oxygen vs. Sulfur. Redox Potentials for Some Pyrylium and Thiapyrylium Salts
Saeva, F. D.,Olin, G. R.
, p. 299 - 303 (1980)
The redox levels for two series of pyrylium and thiapyrylium salts were measured by cyclic voltammetry.This information was utilized to provide a quantitative comparison of the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) which is a measure of the thermodynamic stabilities to electron transfer of oxygen vs. sulfur adjacent to carbon cation, radical, and anionic centers in a single system.In one of the series dicationic, cationic, radical, and anionic centers were compared.The ionic and radical species were found to be thermodynamically more stable in the sulfur analogue (less stable in oxygen analogue) in every case except when the HOMO and/or LUMO level is localized on the diethylaminophenyl moiety.The order of the greatest sulfur preference or least oxygen preference is the following: anion>radical and radical>cation for the HOMO and LOMO levels, respectively.The wavelength of the intramolecular charge transfer band and the electrochemical reduction potentials indicate that the thiapyrylium moiety is more electron withdrawing than pyrylium.
Radical alkylation of isocyanides with amino acid-/peptide-derived Katritzky salts via photoredox catalysis
Zhu, Ze-Fan,Zhang, Miao-Miao,Liu, Feng
, p. 1531 - 1534 (2019)
An efficient and mild method was developed for the synthesis of 6-alkylated phenanthridines upon visible light irradiation. Bench-stable and easily handled redox-active Katritzky pyridinium salts derived from abundant amino acids/peptides were used as radical precursors for the alkylation of isocyanobiphenyl species. The reaction displays an excellent functional group tolerance and a potential utility for peptide functionalization, allowing access to desired products in good to excellent yields.
Dissection of alkylpyridinium structures to understand deamination reactions
Tcyrulnikov, Sergei,Cai, Qiuqi,Cameron Twitty,Xu, Jianyu,Atifi, Abderrahman,Bercher, Olivia P,Yap, Glenn P. A.,Rosenthal, Joel,Watson, Mary P.,Kozlowski, Marisa C.
, p. 8456 - 8466 (2021)
Via conversion to Katritzky pyridinium salts, alkyl amines can now be used as alkyl radical precursors for a range of deaminative functionalization reactions. The key step of all of these methods is single-electron reduction of the pyridinium ring, which triggers C-N bond cleavage. However, little has been done to understand how the precise nature of the pyridinium influences these events. Using a combination of synthesis, computation, and electrochemistry, this study delineates the steric and electronic effects that substituents have on the canonical steps and the overall process. Depending on the approach taken, consideration of both the reduction and the subsequent radical dissociation may be necessary. Whereas the electronic effects on these steps work in opposition to each other, the steric effects are synergistic, with larger substituents favoring both steps. This understanding provides a framework for future design of pyridinium salts to match the mode of catalysis or activation.
Continuous-Flow Synthesis of Pyrylium Tetrafluoroborates: Application to Synthesis of Katritzky Salts and Photoinduced Cationic RAFT Polymerization
Sambiagio, Carlo,Ferrari, Matteo,Van Beurden, Koen,Ca', Nicola Della,Van Schijndel, Jack,Noel, Timothy
supporting information, p. 2042 - 2047 (2021/04/05)
Katritzky salts have emerged as effective alkyl radical sources upon metal- or photocatalysis. These are typically prepared from the corresponding triarylpyrylium ions, in turn an important class of photocatalysts for small molecules synthesis and photopolymerization. Here, a flow method for the rapid synthesis of both pyrylium and Katrizky salts in a telescoped fashion is reported. Moreover, several pyrylium salts were tested in the photoinduced RAFT polymerization of vinyl ethers under flow and batch conditions.
C-H Alkylation of Aldehydes by Merging TBADT Hydrogen Atom Transfer with Nickel Catalysis
Murugesan, Vetrivelan,Ganguly, Anirban,Karthika, Ardra,Rasappan, Ramesh
supporting information, p. 5389 - 5393 (2021/07/21)
Catalyst controlled site-selective C-H functionalization is a challenging but powerful tool in organic synthesis. Polarity-matched and sterically controlled hydrogen atom transfer (HAT) provides an excellent opportunity for site-selective functionalization. As such, the dual Ni/photoredox system was successfully employed to generate acyl radicals from aldehydes via selective formyl C-H activation and subsequently cross-coupled to generate ketones, a ubiquitous structural motif present in the vast majority of natural and bioactive molecules. However, only a handful of examples that are constrained to the use of aryl halides are developed. Given the wide availability of amines, we developed a cross-coupling reaction via C-N bond cleavage using the economic nickel and TBADT catalyst for the first time. A range of alkyl and aryl aldehydes were cross-coupled with benzylic and allylic pyridinium salts to afford ketones with a broad spectrum of functional group tolerance. High regioselectivity toward formyl C-H bonds even in the presence of α-methylene carbonyl or α-amino/oxy methylene was obtained.
